The invention relates to a method of measuring the attenuation in optical waveguides. A light transmitter feeds energy into the waveguide, and a receiver receives the light output from the end of the waveguide. The transmitter radiates light pulses into the waveguide and the receiver receives the light as an average value.
To measure the attenuation of optical wave-guides, it is known to measure the output power of a light transmitter in the input of the fiber, to switch the optical fiber to be measured into the circuit, and to repeat the measuring operation. The resultant level change is a measure of the attenuation of the optical fiber. This method is particularly suitable for use during measurements on single waveguide conductors and on cables during and after fabrication.
Another known method is commonly referred to as the cut-back method, in which the optical fiber to be measured is connected to a coupling fiber, and the light output at the fiber end is determined with the aid of a systems receiver. Then, the optical fiber to be measured is cut in the region of the coupling fiber, and the optical power transmitted through this cut off short section is measured. The attenuation in the optical fiber can be determined from the resultant power difference between these two measurements.
If very accurate measurements are desired, then one must check during the measuring operation whether the transmitter power fluctuates. Particularly when the two measurements are made at different times, the transmitter power fed into the fiber may change, so that the measuring results do not accurately correspond to the actual attenuation value.
One may consider monitoring, when measuring the optical power out of the fiber, the transmitter power fed into the fiber and to transmit the data to the receiving station when the transmitter and the receiver are located in positions remote from each other, for example in the case of a cabled network.
It is alternatively possible to arrange a reference line in parallel with the installed cables to be measured, and to feed the same amount of energy into these two lines. The attenuation of the reference line being known, the attenuation of the cables to be measured can be properly determined, even when the transmitter power fluctuates.
The above-mentioned, known or proposed methods either produce inaccurate results, or require considerable design effort and cost, or cannot be implemented under certain circumstances, for example because it is not possible to install an additional reference line in the section to be measured.